Just cause I like correcting you – See http://en.wikipedia.org/wiki/Power_symbol No one really knows where it comes from. And since I am an engineer, I would probably lean towards “Another explanation is that “1” represents a closed switch and “0” represents an open switch, in common with engineering diagrams.” Especially since switches were a lot more common back when as compared to binary. Although in the end I know you are going to come back at me with its the chicken and the egg scenario.